Erin Biba in Wired:
Lene Vestergaard Hau can stop a pulse of light in midflight, start it up again at 0.13 miles per hour, and then make it appear in a completely different location. “It’s like a little magic trick,” says Hau, a Harvard physicist. “Of course, in all magic tricks there’s a secret.” And her secret is a 0.1-mm lump of atoms called a Bose-Einstein condensate, cooled nearly to absolute zero (-459.67 degrees Fahrenheit) in a steel container with tiny windows. Normally — well, in a vacuum — light goes 186,282 miles per second. But things are different inside a BEC, a strange place where millions of atoms move — barely — in quantum lockstep.
About a decade ago, Hau started playing with BECs — for a physicist, that means shooting lasers at them. She blew up a few. Eventually, she found that lasers of the right wavelengths could tune the optical properties of a BEC, giving Hau an almost supernatural command over any other light shined into it. Her first trick was slowing a pulse of light to a crawl — 15 mph as it traveled through the BEC. Since then, Hau has completely frozen a pulse and then released it. And recently she shot a pulse into one BEC and stopped it — turning the BEC into a hologram, a sort of matter version of the pulse. Then she transferred that matter waveform into an entirely different BEC nearby — which emitted the original light pulse. That’s just freaky. Hey, Einstein may have set that initial speed limit of light, but he only theorized about BECs. “It’s not breaking relativity,” Hau says. “But I’m sure he would have been rather surprised.”